...
- MSR's Monsoon vs. UCSD's Fat-Tree commodity system
- Want network connecting many 1GigE nodes with no oversubscription
- MSR uses a hierarchical configuration (10GigE aggregation and core switches, 1GigE TOR switches)
- UCSD's uses identical, 24-port, commodity 1GigE switches (i.e. k = 48)
- Both theoretically capable of 1:1 oversubscription (i.e. no oversubscription)
Hierarchical
Fat-tree
# hosts
25,920
27,648
# switches
108 x 144-port 10GigE
1,296 x 20-port 1GigE w/ 2x10GigE uplinks2,880 x 2448-port 1GigE
# wires
57,024 (~91% GigE, ~9% 10GigE)
82,944
# unique paths
144 (36 via core with 2x dual uplinks in each subtree)
572
- Notes:
- 48-port 1GigE switches cost ~$2.5-3k
- 2,880 * $2500 = $7M
- 20-port 1GigE switches w/ 10GigE uplinks probably cost about the same (~2.5-3k) [uplinks not commodity]
- 1,296 * $2500 = $3.24M
- 144-port 10GigE switches advertised as $1500/port ($216k/switch) in mid-2007
- to be competitive with fat-tree on per-port cost, price per port must drop 6.25x to $241.76 ($34.8k/switch)
- 6.25x drop seems pretty close to the common 2-year drop in price
- 48-port 1GigE switches cost ~$2.5-3k
- Notes:
Misc. Thoughts
- If networking costs only small part of total DC cost, why is there oversubscription currently?
- it's possible to pay more and reduce oversubscription - cost doesn't seem the major factor
- but people argue that oversubscription leads to significant bottlenecks in real DCs
- but, then, why aren't they reducing oversubscription from the get go?